Separation of aldehydes from aliphatic hydrocarbons by azeotropic distillation with perfluorocompounds



Patented Jan. 26, 1954 2,667,450 'SEP-ARKTiO'N or ALDEHYDES ETROMAH' 'RH IQ TRoPIo Di'STILLATIGN WITH run-'- FLUOR'OCOMPOUNDS Martin R. Cines, Kngxville, Tenn assignor to lhillips Petroleum Company, a corporation of Delaware No brewing. Application sugust'14,' 1 95 '1=,

Serial No. 241- 899 3 Claims. 1

This invention relates to a new "process for the separation of solutions of liquid mixtures of aldehydes from aliphatic hydrocarbons having vapor pressures which are substantially the same, or which form azeotropic mixtures, and the complete separation of which by ordinary fractionation methods is, for these reasons, extremely difficult and often impossible. In one of its aspects the invention relates to the employment of an entrain'er whereby the desired separation can be accomplished.

I have now found a new method or manner for removing or separating aldehydes from aliphatic hydrocarbons. This new method. removes the aldehydes by means of azeotropic distillation in the presence of an entrainer selected from the group of non-acidic organic periiuoro-compounds. The aldehydes are removed as overhead and the aliphatic hydrocarbons removed as a kettle product. Ordinary azeotropic distillation equipment can be used in efiecting this process.

Entrainers according to this invention are non-- acidic organic perfluoro-compounds such as perfiuoro-n-heptane and perfiuoro-methylcyclohexane, and other compounds such as perfluorodi-nbutyl ether, perfiuoro-tri-n-propylamine and perfluoro-tri-n-buty1amine. Other compounds Within the defined group are satisfactory. It is desirable to employ an entrainer having a boiling point within 70 F., preferably 35 F., of the aldehyde. Entrainers having boiling points over 75 'F. from that of the aldehyde to be removed are less effective and sometimes completely ineffective. It is preferable that when aliphatic hydrocarbon mixtures are to be processed by this invention for the removal of aide hydes, that the boiling range of the hydrocarbon out should not be over 50 F. and is more :preierably not over 25 F.

The operation of this, process is quite similar to the usual azeotropic distillation process in that the entrainer and the hydrocarbon mixture to be purified are charged to a fractionating column; the aldehyde azeotrope is removed overhead and the purified hydrocarbon is removed as a kettle product. The entrainer is then recovered from the overhead product and recycled to the column for further use. No consumption of the entrainer other than normal handling losses is encountered.

Some ketones can likewise be removed from aliphatic hydrocarbons through the use of perfluoro compounds as entrainers.

The following two examples are illustrative of the efiectiveness of this process. The tests were carried out in a small distillation column consisting of a two foot section of glass tubing approximately 6 mm. inside diameter and containing a single wire spiral for packing. The column was insulated by a vacuum jacket and equipped with a suitable kettle and a total condensing head with the liquid takeofi".

EXAMPLE I Azeotropic distillation data Overhead data Charge System BonnolgFpomt volume, Composipercent tion, Temp., Liquid volume F. phases Percent Isovaleraldehydel 198. 5 33. 3 23. 1 2-3 dimethylpentana. 198. 5 33. 3 6. 9 155 2 Perfluoro-n-heptane 181. O 33. 4 70. 0

EXAMPLE II Overhead data Charge System BofluolgFpomt' volume, Composipercent tion, Temp., Liquid volume F. phases percent l-pentanal 216 (744 mm.)---- 33.3 26.6 2,2,4-trimethylpen 214 33.3 13.4 1 177-133 2 Perfluorodimethylcyclohexane. 214 33.4 60. 0

1 A plateau was obtained from 178.7 to 179.0" F.

The above data were obtained at atmospheric pressure. In carrying out the test, the kettle was charged with the hydrocarbon and the aldehyde along with a small amount of the entrainer. The column was then started in operation and when equilibrium was reached, an overhead sample was taken. The overhead product from each of these two tests was homogeneous at the boiling point, but it was a two phase mixture at room temperature.

The efiectiveness of this class of entrainers is quite evident from the foregoing tests. Even though the aldehyde and the aliphatic hydrocarbons were close boiling, the very low efiiciency column (about five theoretical plates or less) effected quite substantial concentration of the aldehyde in the overhead product based on the entrainer-free material.

Reasonable variation and some modification are possible within the scope of the foregoing disclosure and the appended claims to my contribution to the art the essence of which is that nonacidic organic perfluoro compounds have been found to be highly effective for the removal by distillation of aldehydes from mixtures of them with closely boiling aliphatic hydrocarbons.

I claim:

1 1. The separation of difiicultly separable liquid mixtures of aliphatic aldehydes from aliphatic 4 hydrocarbons, by using an entrainer selected from the group consisting of perfiuoro-n-heptane and perfiuoro-methy1cyc1ohexane, perfiuoro-din-butyl ether, perfluoro-tri-n-propylamine and perfluoro-tri-n-butylamine and subjecting said mixtures to distillation.

2 The separation by distillation of a mixture of an aliphatic aldehyde and an aliphatic hydrocarbon which are difficultly separable by distillation which comprises the steps of admixing with said mixture an entrainer selected from the grou consisting of perfiuoro-n-heptane, perfiuoro-methylcyclohexane, perfiuoro-di-n butyl ether, perfiuoro-tri-n-propylamine and perfiuoro-tri-n-butylamine and subjecting the admixture thus obtained to distillation.

3. The separation of l-pentanal and 2,2,4-trimethylpentane by admixing therewith perfluorodimethylcyclohexane and subjecting the admixture thus obtained to distillation.

MARTIN R. CINES.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,050,235 Othmer Aug. 4, 1936 2,376,870 Engel May 23, 1945 2,442,589 Evans et a1. June 1, 1948 

1. THE SEPARATION OF DIFFICULTY SEPARABLE LIQUID MIXTURES OF ALIPHATIC ALDEHYDES FROM ALIPHATIC HYDROCARBONS, BY USING AN ENTRAINER SELECTED FROM THE GROUP CONSISTING OF PERFLUORO-N-HEPTANE AND PERFLUORO-METHYLCYCLOHEXANE, PERFLUORO-DIN-BUTYL ETHER, PERFLUORO-TRI-N-PROYLAMINE AND PERFLUORO-TRI-N-BUTYLAMINE AND SUBJECTING SAID MIXTURES TO DISTILLATION. 